The invention relates to a seal between static parts of a turbine.
Such seals are used primarily in gas turbines. They are used as seals between static parts of the turbine, for example in cooling air paths of guide vanes, between the individual segments of a series of guide vanes, or as a circumferential seal between a housing part of the turbine and a guide vane.
This type of seal is described for example in U.S. Pat. No. 5,743,708, and is shown in particular in FIGS. 17 and 18 of this document. The seal in this case consists of a flat metal piece provided on each of two opposite sides with a solid bead. When viewed as a cross-section, the seal has a long, narrow middle piece, which at each of its ends has a round bead. Because of its cross-section, it is called a xe2x80x9cdog bone sealxe2x80x9d. In the first series of guide vanes, it is located in each case between adjoining guide vane platforms, and functions there as a seal for cooling air paths in order to cool the outside and inside platforms of the guide vanes.
Each of the individual solid, round beads is located in a groove of adjoining guide vane platforms, whereby these beads rest snugly against the inside surfaces of the grooves. Each of the seals extends over the lateral length of a platform. The seal is achieved primarily by a pressure differential, whereby the seal occurs along lines on the lateral surfaces of the grooves where the rounded beads contact the flat inside surfaces of the grooves. A seal hereby must be ensured by the beads in both grooves.
A variation of this type of seal, a so-called xe2x80x9cdog bone sealxe2x80x9d is disclosed in U.S. Pat. No. 5,868,398. It also functions as a seal between adjoining guide vane segments in this case. However, the bead at the sides of the seal is not constructed in a solid manner, but is realized by a curvature of the flat metal piece, whereby the curved parts are set into a groove.
Another variation of this seal is a circumferential seal, for example, for sealing the rotor hood of the turbine against the first guide vane series in order to create a seal between cooling air and hot gas.
In this seal, the flat metal piece has the form of a ring provided at its radially inward and its radially outward side with a bead. Each of the static parts is provided with a groove in which the beads are arranged. The metal ring of these seals consists of at least two parts, for example, two 180xc2x0 parts, which seal against the lower or respectively upper half of the turbine. The beads contact the insides of the grooves along an arched line extending over 180xc2x0.
These seals have the disadvantage that in the absence of an adequate pressure differential, there is an insufficient contact of the beads, resulting in a leak. Furthermore, the seal is not fully ensured if one or both static parts of the turbine shift axially, and the grooves shift relative to each other. In this case, a crescent-shaped space is created along each of the two 180xc2x0 segments between a groove and the bead located inside it, resulting in a leak. In order to prevent such leaks resulting from a relative shifting of the grooves, the seals may be realized in several shorter ring segments, for example. In this case, the contact line between beads and groove surfaces is always an almost straight line instead of a curved line. This makes it possible that the seal is able to rock back and forth inside the grooves, and if the grooves shift, the seal is able to move with them, whereby a continued contact, i.e. the seal, is ensured along the straight line. However, leaks may occur at the joints between the individual ring segments so that overall improvement of the seal is questionable.
In view of the cited disadvantages of the initially described seal, the invention is based on the objective of creating a seal of this type between static parts of a turbine, said seal ensuring a sufficient seal at all times, with this seal resulting not exclusively from a pressure differential, and where said seal retains its sealing effect during a relative shifting of the static parts.
A seal between static parts of a turbine is provided with a first carrier piece comprising a flat metal piece, having a middle piece and two end pieces, whereby said end pieces are arranged at opposite sides of the carrier piece, and where each of said end pieces extends over the entire lateral length. The carrier piece extends over the space to be sealed between the static parts of the turbine, whereby each of the end pieces is arranged in grooves inside the static parts. According to the invention, the seal has a second part comprising a flat metal piece arranged parallel to the carrier piece and attached to the carrier piece. It also has a middle piece and two end pieces, whereby its end pieces are also arranged in the grooves on the static turbine parts. Hereby at least one end piece in each groove is constructed in a resilient manner, i.e. either the end piece of the carrier piece or of the second part, or both. Each of the resilient end pieces is force-fitted in the grooves.
The resilient characteristic of the end pieces causes the latter to be snugly force-fitted against the surfaces of the grooves, resulting in a seal along the contact line between end pieces and grooves. The forced contact and seal are substantially independent from a pressure differential. The resilient characteristic furthermore has the result that, in the case of a shifting of the grooves relative to each other, the end pieces continue to rest against the groove surfaces in a force-fitted manner along contact lines. As a result no spaces form between grooves and end pieces and a seal is ensured even if the static parts shift.
In a first embodiment of the seal according the invention, the end pieces of both the carrier piece as well as the end pieces of the second part are designed in a rounded and hook-shaped manner, whereby the inside of the hook shape of the end pieces on the carrier piece faces the second part, and the inside of the curvature of the hook shape of the end pieces of the second part faces the carrier piece. The hooks of the end pieces of both parts therefore run towards each other. Hereby their length is such that they extend inside each other.
In a preferred embodiment, the flat metal piece of the second part is constructed thinner than that of the carrier piece. This increases the resilient effect of the end pieces of the second part. Depending on the application and extent of the expected relative shifting of the grooves, the thickness of the metal piece for the second part can be chosen so the necessary resilient effect is achieved.
In this first embodiment, a carrier piece consists of two ring segments of 180xc2x0 each. The second part in each case consists of several short ring segments that are attached along the carrier piece.
In a variation, the second part also consists of two ring segments of 180xc2x0 each. In yet another variation, the carrier piece as well as the second part consists of several short ring segments.
In a further preferred embodiment, the second part is attached at the carrier piece in a slightly offset manner so that it projects beyond the edge of the carrier piece and overlaps the adjoining carrier piece at the joint between the ring segments. This prevents a leak at the joints.
In a variation of this embodiment, the ring segments of the seal have the circumferential length of a single guide vane platform, for example, in its application for sealing the space between guide vane platforms and the inner housing. In the case of short segments, the contact lines between end pieces and grooves are straight. This makes it possible that in case of a relative shifting of the grooves the sealing ring segments are able to rock back and forth within theses grooves, and a contact and seal is maintained. In order to achieve a seal between the individual ring segments, the carrier pieces in this case are constructed so that they overlap each other at the joints.
In a second embodiment of the invention, a carrier piece consists of a seal with middle piece and end pieces, whereby the end pieces are solid beads. The second part of the seal consists of a flat metal piece that is provided at its sides with end pieces constructed in a resilient manner. Each of the resilient end pieces is constructed in an acutely angled roof shape. The tip of these end pieces in each case touches the insides of the grooves, forming the seal. In a variation, the resilient end pieces are also constructed in hook shape here. Depending on the extent of the shifting of the grooves and on the properties of the grooves, the size of the segments of the carrier piece and of the second part of the seal have been chosen accordingly here also.